Fairly large numbers of Chalkhill Blues feeding on various purple flowers on chalk grassland slopes.
No interactions present.
The female on the bottom left looks very like a female adonis to me, but they don't occur at this site so it must be a chalkhill. The 2 species are very difficult to separate, and at some sites can be both on the wing this week. This specimen is certainly very blue for a female chalkhill - although there is a great deal of variation. To be absolutely certain you would have to get a close look at the pale rings on the rear edge of the upper hind-wings. If the lightest margin towards the rear is white, then it's a chalkhill; if there is any blue here it's an adonis. See my photo at http://www.ispot.org.uk/node/3798
I did look closely at the Adonis and the Chalkhill when identifying the female. I concluded Chalkhill because there were no signs of blue scales in the pale rings on the hind wing, although the photo at the resolution I've provided might not be convincing. If the undersides are useful, it's the same female in both pictures and I think the male is the same individual too. I wasn't sure if the Adonis had been recorded on the site or not, but I certainly didn't see any males.
There were Brown Argus there too, but they were smaller, had far more orange spots around the wing edges and no signs of any blue scales.
Yes, on closer inspection it clearly is a chalkhill, for the reasons you give above. Still a very bright one though.
Lat/Lng: 51.958772665367, -0.44986009597778
OS grid ref: TL066300
Ancient beech woodland and chalk grassland. Fields are regularly grazed by sheep, with some areas protected by woodland, scrub or steep gradients. Owned by the National Trust with free public access to an extensive network of footpaths.